The present invention relates to a coloring layer composition for a chromatic device, and a method of producing a chromatic device by using the composition. The composition can be used in, for example, a coloring layer formation process for forming a reduction coloring layer of an electrochromatic (EC) device.
A known chromatic device, e.g., EC device, comprises a first transparent substrate 1, a first electrode layer 2, a reduction coloring layer 3, an electrolyte layer 4, an oxidation coloring layer 5, a second transparent electrode layer 6 and a second transparent substrate 7, which are successively laminated as shown in FIG. 1. In this EC device, when a current higher than the determined threshold value is applied between the first electrode layer 2 and the second electrode layer 6, oxidation and reduction reactions take place in the vicinities of the interfaces between the first electrode layer 2 and the reduction coloring layer 3 and between the second electrode layer 6 and the oxidation coloring layer 5 to obtain a reversible coloration-bleaching change.
In the EC device, tungsten oxide (WO.sub.3) can be used for the reduction coloring layer 3. Known methods of forming the reduction coloring layer 3 comprising WO.sub.3 include general dry methods such as a sputtering method and an evaporation method, a spin coating method for forming a film by using a peroxotungstic acid solution as disclosed in "Applied Physics" No. 61, Vol. 3 (1992) (pp. 226-269), and a dip coating method for forming a film by using the some peroxotungstic acid solution. Other known methods of forming the reduction coloring layer in the EC device include methods using a solution containing an organic compound of W, as disclosed in Japanese Patent Laid-Open Nos. 56-38379, 61-36292, 61-123691 and 62-112132.
However, if a dry method such as a sputtering or evaporation method is performed, a large vacuum apparatus is required for obtaining a large-area EC device, thereby increasing the production cost. Particularly, if the sputtering method is executed, since the temperature of the substrate used is increased, a glass substrate can be used, but a resin substrate cannot, thereby hindering the light weight properties of the EC device.
Even if the spin coating method is performed, the coloring layer can be obtained without an increase in the production costs only when a substrate of about 30 cm square is rotated, and thus larger EC device cannot be produced at low cost.
It thus seems practically effective when producing a large EC device at low cost to perform the dip coating method. Wet methods such as printing methods, spray methods, spin coating methods and so on other than the dip coating method also seem to be practically effective.
However, the results of the tests performed by the inventors showed that the wet dip coating method causes wave-like flows in the film after pulling up the substrate, and thus causes unevenness in the reduction coloring layer formed by drying the film as is. Particularly, if the peroxotungstic acid solution is used in the dip coating method, bubbles occur in the film due to the generation of oxygen caused by the decomposition reaction of the hydrogen peroxide contained in the solution, and the release of the oxygen dissolved therein during the dipping and pulling-up of the substrate. If the film is dried as is, unevenness occurs in the reduction coloring layer formed. Since the unevenness in the reduction coloring layer can be visually confirmed, and as it causes unevennes in the transmittance of the EC device during coloring, quality problems arise.
In addition, although a uniform film can be formed immediately after pulling up the substrate, heat treatment of the film in post-processing causes cracks in the reduction coloring layer and in turn separation of the layer. The cracks and separation bring about contact between the electrolyte layer and the first electrode layer of the EC device, thereby causing quality problems due to deterioration or dissolution of the first electrode layer. If a large EC device is produced, unevenness in or separation of the reduction coloring layer is particularly conspicuous, and utility thus significantly deteriorates. A wet method using a solution containing an organic compound of tungsten has the drawback that preparation of the organic compound is troublesome.
The above drawbacks apply to not only the EC device but also other chromatic devices such as thermochromatic devices, photochromatic devices and so on which have a coloring layer comprising an oxide of at least one of W, Nb, Mo and V.
The present invention has been achieved in consideration of the above actual conditions, and an object of the present invention is to permit reliable production of a large chromatic device at low cost.
Another object of the present invention is to provide a novel coloring layer composition used for forming a reduction coloring layer of a chromatic device.
A further object of the present invention is to provide a high-quality chromatic device on which a coloring layer is formed by using the above composition under specified conditions so as to prevent unevennes in and separation of the coloring layer.
As a result of intensive studies performed by the inventors for solving the above problems, it was found that the mixing of an organic solvent with a coloring layer forming composition is effective for decreasing the surface energy of the film formed and effective in preventing unevenness in and separation of the film. It was also found that the organic solvent can prevent oxygen from generating due to the decomposition of hydrogen peroxide, and in prevent the dissolved oxygen from being released. The organic solvent is required to have compatibility with water because a solute comprising an oxide of at least one of W, Nb, Mo and V is dissolved in water, and to be evaporated by heat treatment of the film. This resulted in the achievement of the present invention. It was further found that a film of a coloring layer without unevenness or separation can be formed by employing a dip coating method and vertically pulling up the treated substance at a low speed.